The 110 v. outlet or receptacle (often called “duplex” because it has jacks for two two- or three-pronged plugs) is a staple of modern American living, found on walls in nearly every occupied space. Nearly every 110 v. AC portable electrical device is designed to temporarily plug into a duplex outlet for power. Outlets are typically wall-mounted, with the outlet and a surrounding cover plate projecting slightly from the surrounding surface.
For safety purposes, electrical codes require specific installation formats for duplex outlets. Without exception, every duplex outlet must be mounted in an electrical box that is firmly attached to a part of the building structure such as wallboard or a stud, and within the space between studs or, less frequently, joists. Wiring led through the spaces between studs or joists enters the electrical boxes through holes provided therein and connects to terminals of the outlets.
The electrical box serves to anchor the outlet to the building structure and provides a mechanical barrier between the connections to the outlet and nearby combustibles. Experience shows that many electrical problems arise in the connections between the outlet and the electrical wiring. Placing these connections within an electrical box will often prevent heat generated by a faulty wiring connection from starting a fire. It also prevents mechanical damage to the connection and the outlet.
The most common type of duplex outlet has two mounting holes spaced approximately 3¼ in. apart. Electrical boxes have a mounting hole on each two facing walls, spaced to mate with the outlet mounting holes. The electrical box mounting holes receive threaded machine screws that pass through the outlet mounting holes to firmly affix the outlet to the box. Other types of outlet mounting are sometimes used as well.
Other types of electrical connectors such as telephone and Ethernet jacks and coaxial cable terminations also have a mounting format compatible with standard electrical boxes. This provides a convenient way to anchor these connectors to the structure even if no safety issue is present for these low voltage connectors.
For purposes of generality, the intent is that the term “outlet” in this specification refers to all of these different kinds of signal and power voltage jacks and connectors.
In many ways, these standard outlets serve admirably. They are safe, have been standardized throughout the United States, and are relatively inexpensive. These outlets have a number of disadvantages however.
One problem with standard outlets is simply aesthetics. Their appearance is strictly utilitarian. Designer cover plates compensate poorly for this lack.
More importantly, standard power outlets provide a risk of physical harm to children, who may poke conducting objects into the hot terminal of such outlets. And in public spaces, standard receptacles may be vandalized. Further, exposed outlets may be inadvertently damaged during cleaning or when bumped by heavy objects.
Lastly, outlets on outside walls in colder climates may form a bypass that allows cold air to leak into the occupied space.
For all of these reasons standard outlets are not suitable for all locations.